Geography · Ch 6 — Natural Hazards and Disasters
Consequence and Control of Floods
Consequence and Control of Floods
The map is a flood-hazard map of India, and its entire purpose is to show you where floods actually happen, not just to list rivers. The shaded areas — labelled "Area Liable to Flood" — are the visual heart of the diagram. They cluster along the river systems that drain the northern and eastern parts of the country, and the pattern is not random: it follows the path of water moving from the mountains to the sea.
Look first at the northwest. The Punjab river-tributary belt is shaded — the Indus system's five rivers (Jhelum, Chenab, Ravi, Beas, Sutlej) and the land between them. This is the flash-flood zone, where sudden, intense rainfall or snowmelt in the hills sends a wall of water down narrow channels. The shading here is thinner, more linear, because the floods are quick and localised rather than widespread.
Then comes the great Ganga plain. The shaded corridor runs from Delhi eastward through Uttar Pradesh, Bihar, and into West Bengal — a continuous band that tracks the Ganga and its major tributaries (Yamuna, Ghaghara, Gandak, Kosi). This is the most extensive flood zone on the map, and it makes sense: the plain is flat, the rivers carry enormous sediment loads, and they shift course and spill over their banks every monsoon. The Kosi, in particular, is notorious for changing its channel entirely.
The Brahmaputra valley in Assam is a separate, dense patch of shading. The map shows the river and its tributaries — the Dibang and the Lohit are labelled explicitly — converging into the main channel. This is a valley hemmed in by hills on both sides, so when the river floods, there is nowhere for the water to go but over the floodplain. The shading here is broad and solid, reflecting the annual, near-certain inundation that Assam experiences.
Finally, there are coastal patches along the eastern seaboard — near the Mahanadi delta in Odisha and the Krishna–Godavari deltas in Andhra Pradesh. These are not river floods in the same sense; they are storm-surge floods, driven by cyclones pushing seawater inland. The shading is smaller and more fragmented than the Ganga corridor, but it marks a distinct hazard: the sea itself becomes the flood source. …
Floods are usually seen only as disasters, but the chapter asks you to look at them with a fuller eye — what they destroy, what they occasionally give back, and what governments actually do about them. The consequences are overwhelmingly negative, yet a small positive side exists, and the control measures are a mix of engineering, planning, and common sense.
Consequences of Floods
The damage from floods is not spread evenly across India. Different regions face different kinds of flooding, and the book names them specifically:
- Riverine flooding hits Assam, West Bengal, Bihar, and eastern Uttar Pradesh, where rivers overflow their banks.
- Coastal flooding from cyclones affects Odisha, Andhra Pradesh, Tamil Nadu, and Gujarat, where storm surges push seawater inland.
- Flash floods strike Punjab, Rajasthan, northern Gujarat, and Haryana, where sudden heavy rain overwhelms dry, hard ground.
The consequences ripple through both the economy and society:
- Crops are destroyed every year, which is a direct blow to farmers and to national food supply.
- Physical infrastructure is damaged — roads, railways, bridges, and human settlements all take a hit.
- People lose their homes and lives. Millions are rendered homeless, and people are washed away along with their cattle.
- Disease spreads in the aftermath. Cholera, gastro-enteritis, hepatitis, and other water-borne diseases become common in flood-affected areas.
The book lists these diseases specifically — cholera, gastro-enteritis, and hepatitis. These are water-borne, not water-contact, diseases. That distinction matters for understanding why they spread after floods: contaminated drinking water, not just standing water.
The Positive Side of Floods
Floods are not entirely destructive. The book is careful to note two genuine benefits:
- Fertile silt is deposited over agricultural fields every year, which enriches the soil and is good for crops.
- Majuli in Assam, the largest riverine island in the world, is the best example. It produces good paddy crops because of the annual floods of the Brahmaputra, not despite them.
But the book immediately qualifies this: these benefits are insignificant compared to the grave losses floods cause. The silt is a consolation, not a compensation.
Majuli (Assam) is the largest riverine island in the world — this is a fact worth remembering, and it is tied directly to the positive role of annual flooding.
Control of Floods
The Government of India and state governments are well aware of the menace, and the book lists the steps that need to be taken on an urgent basis:
- Construction of flood protection embankments in flood-prone areas.
- Construction of dams to regulate river flow.
- Afforestation in the upper reaches of flood-creating rivers.
- Discouraging major construction activities in the upper reaches of these rivers.
Two further steps are suggested, and these are particularly relevant for the flash-flood regions:
- Removal of human encroachment from river channels. …
According to an estimate of the Rashtriya Barh Ayog (National Flood Commission), 40 million hectares of land is flood prone in the country. Assam, West Bengal and Bihar are among the high flood-prone states of India. Apart from these states, most of the rivers in the plains of Punjab and Uttar Pradesh are also vulnerable to occasional floods. In recent decades, most of the states of India have experienced flash floods, which have inflicted heavy loss of life and property. States like Rajasthan, Gujarat and Haryana, which experience low rainfall and drought-like conditions, are also vulnerable to flash floods due to variability in monsoon rainfall, and blockage of natural drainage channels by human activities. Occasionally, retreating monsoon brings flooding in the state of Tamil Nadu, particularly during November and January months.
Flood-prone regions and their associated causes may be grouped as: (i) Assam, West Bengal and Bihar; the north Bihar and eastern Uttar Pradesh are the most flood prone areas due to the rivers flowing down from the Himalayas; (ii) Coastal Odisha, Andhra Pradesh, Tamil Nadu and Gujarat, due to cyclones; (iii) Punjab, Rajasthan, northern Gujarat and Haryana, due to flash floods.
Floods disrupt physical infrastructure, like roads, rails, bridges and human settlements, causing collapse of houses, walls, electric/telephone poles etc. leading to loss of life and property. Millions of people are rendered homeless and are also washed away along with their cattle in flood water. Excess flood water gets contaminated due to intermixing with sewage and other wastes, and this contamination becomes the breeding ground for water-borne diseases like cholera, gastro-enteritis and hepatitis. Floods, at times, also do some good to the land, e.g. they deposit fertile silt on agricultural fields which enriches the soil. Majuli (Assam), the largest riverine island in the world, is the best example of good paddy crop after every flood in the Brahmaputra river. However, these benefits are insignificant as compared to the amount of damage that flood causes to agriculture, human settlements, physical infrastructure and human life. …